1. Field of the Invention
The present invention relates to a method, computer readable medium and apparatus for converting color image resolution, and more particularly relates to a method, computer readable medium and apparatus for converting color image resolution to convert relatively low resolution color image having bi-level and multi-level pixel values into relatively high resolution color image.
2. Discussion of the Background
In general, a digital image displayed on a monitor screen, such as an image of an Internet web page, has relatively low image resolution, for example, 72 dots per inch (dpi). On the other hand, recent color image printers can print images with a relatively high image resolution such as 400 dpi, 600 dpi, 1200 dpi, etc., in comparison with such the monitor screen. In other words, a printed image can have more picture elements (pixels) than an image displayed on such the monitor screen per unit area. Therefore, when image data for displaying on a monitor screen is directly printed on a sheet of paper as a hardcopy by the color image printer, the size of the printed image becomes smaller than that on the monitor screen. To print a hardcopy with a preferable size by capitalizing on a high image resolution capability of those color image printers, a relatively low resolution image data is converted into a relatively high resolution image data.
As another example, an image taken by a digital still camera, one of scenes taken by a video camcorder, etc., may also have a low image resolution, and therefore such the images may also be converted into relatively high resolution image data. Then, an image printer can print the image substantially in a full of a paper size. A whole image on a monitor screen generally includes various categories of images, such as text and character strings, text and character strings having shadows, text and character strings processed by a so-called anti-aliening processing, photographs, illustrations, drawings, etc. Images are also categorized into bi-level data images such as ordinary text strings and multi-level data images such as continuous toned photographs.
As background art of the field, some Japanese Laid-Open Patent Publications describe methods and devices that convert a relatively low resolution image into a relatively high resolution image according to an image category, respectively. However, as appreciated by the present inventers, those Patent Publications do not disclose a method for converting an image resolution for an image structured by various types of images with reducing a jaggy image, a coloring and a blurring in a relatively short execution time of the conversion.